This invention involves improvements in methods of injecting treating fluid into low-pressure oil well formations. More specifically, this invention discloses improved methods for treating low-pressure wells utilizing a partially pressure balanced valving system. The known method of treating low-pressure wells with injection fluids utilizes several known treating valves which have spring loaded checkvalve structure for allowing injecting of the fluids in precontrolled amounts into the formations.
This known method is of the type disclosed in U.S. Pat. No. 3,713,490, in the 1964-1965 World Oil Composite Catalog, pages 3680 and 3681, and in the Burt U.S. Pat. No. Re. 22,483. Apparatus useful in the known method of fluid injection is of the type as disclosed in U.S. Pat. Nos. 2,268,010, Re. 22,483, and U.S. Pat. No. 3,802,507.
The above mentioned method and valving devices utilize a coil spring biasing means on a checkvalve member to provide well injection valve service. The basic disadvantage with these devices and their method of operation is that the biasing means utilized must be of sufficient strength to provide a biasing force exceeding the hydrostatic pressure of the column of fluid in the tubing above the valve.
In some of the deeper wells, this results in having to use a very heavy and stiff biasing spring to obtain proper operation of the injection valve. Because of this requirement, the valve usually operates very few times successfully and becomes weakened or breaks during the method of operation.
As an alternative to the extremely heavy and stiff spring, some valve manufacturers have tried to use extremely small valve seat areas to reduce the force of hydrostatic pressure on the spring. Since the resultant downward force on the spring is determined by the pressure above the valve member, multiplied by the cross-sectional area of the valve flow area it is applied to, these designs were made with small flow areas to reduce the downward force of the column of fluid.
While these designs were partially successful in reducing spring failure, they resulted in causing an even greater problem and that involved plugging of the valve flow area. Since most tubing contains some sediment, scale, rust and other foreign matter, the injection of treating fluids and acids down the tubing always breaks loose a quantity of this material which accumulates at the valve mechanism and effectively plugs it up.
The present invention overcomes these disadvantages by providing a method wherein fluid may be injected into a well through apparatus utilizing only a moderate biasing force to hold the hydrostatic pressure of the column of fluid in the tubing. This method utilizes a partial pressure balancing of the valving mechanism to reduce the hydrostatic force on the biasing means and prevent plugging of the valve flow area.